Valve seat inserts are typically installed in aluminum cylinder heads with an interference fit to seal off the combustion chamber from the cylinder head on the backside of the valve, and protect the aluminum cylinder head from damage by the valve seating directly against it. The valve seat must be wear and corrosion resistant at high temperatures, and able to conduct heat away from the valve to be absorbed by the cylinder head. Valve guides, which are also installed in the head with an interference fit, guide the stem part of the valve and so also must be wear resistant, and must be able to conduct heat from the stem to the cylinder head.
Cast iron, brass alloys and sintered powder metal have been used for valve seats. Sintered powder metal finds application to the most severe service, because of its excellent wear, corrosion and heat resistance, and thermal conductivity. However, the components must be made to extremely tight tolerances to achieve a suitable interference fit, and therefore have required machining to remove material from the OD and make the part round and of the accurate diameter. To permit efficient machining, the powder metal alloy of the valve seat or guide has sometimes been formulated to be more machinable, however, at the expense of wear and heat resistance. Even if machinable, it still required machining, which requires additional manufacturing processes and tooling costs.